PLA Woes

My adventure with PLA has ended in heartbreak.  It wasn’t working very well so I switched back to ABS – which was fine for a few prints.  Until I found it just wasn’t extruding and stripping the filament.

So, disassemble time.  My filament looked like it was getting shoved into a jam and splitting apart like a banana – with the center making it down to the nozzle through a small aperture.  I found I couldn’t remove the insulator – and upon looking closer found that a very small amount of PLA had oozed down and around the nut above the insulator/ washer.  I removed the extruder assembly from the ‘bot, and the heater assembly from the extruder, heated it back up and slowly removed the PTFE insulator.  I found the barrel was clogged with ABS as was the insulator.

I’ve managed to clean out most of the insulator, the nut, and the threads of the barrel using drill bits and precision screwdrivers.

I’m going back to ABS, I would rather deal with warp than the heartbreak of PLA ooze into the threads of my heater assembly.

PLA versus ABS, initial thoughts

I’ve yet to print something big as I am still working out some of the black ABS specks from the extruder.  Of the things I have printed so far, it looks like the PLA feels more brittle than the ABS.  ABS will flex slightly when pressure is applied, whereas PLA seems to resist until it snaps.  I like that I’m not wasting PLA by building rafts any more, now that the raft option is turned off in Skeinforge.

PLA takes a little longer to cool which has a few effects on a build.  If the layer underneath is still molten and saggy, the layer on top will sag too.  When an ABS part is done printing you’re basically ready to remove it.  I find that a PLA object can still be a little soft for as much as 15-30 seconds after a build.

I’m loosing finer details on prints.  I just reprinted the toy fire truck swivel.  It turned out really nice except for the actual swivel part.  Unlike the ABS model where the swivel snapped off immediately, the PLA model’s swivel was pretty solid (once it cooled and hardened).  However, it came out too thin!  As I watched it print, the PLA was so warm that it just stretched back during parts of the print – meaning the extruder nozzle made the full circuit, but the plastic stretched a little and pulled back closer to it’s last position.  Uh, that may not sound like the clearest example.

Suffice it to say that small round details such as the swivel didn’t turn out very well.  Which is pretty odd since similar small round detailed parts on the teapot did turn out well.  I suppose part of the reason is the swivel was one small round part where the next hot layer was set down on the prior still hot layer, unlike on the teapot where the thin round spout would be drawn, then the body, then the thin round part for the handle and back over the body – so that by the time the next thin layer was set down the prior layer had cooled.

Skeinforge settings changes

I figured, why not treat this blog as my lab book, right?  It’s a good way to document changes in settings, as well as my rationale for doing so.  Thusly, and without further ceremony, delay, pomp, or ado, I present for your kind consideration and review my latest Skeinforge changes:

  1. Skeinforge->Raft->Activate Raft: checked->unchecked
    • Now that I’m printing in PLA, I won’t need the raft.  As you can probably tell from the pictures below I’ve covered my acrylic build base in blue painter’s tape.  I think I’ll probably just take one of my spare foamcore build surfaces and cover that with blue tape and give that a shot.  I’ve noticed that as soon as my extruder heats up the PLA starts to ooze out.  This isn’t a problem as far as I can tell.  However, it does let some PLA drip – but when I start to run the extruder again it doesn’t extrude at all.  My guess is that the oozing PLA is dripping out of the nozzle, which then has to be filled back up to extrude.  ANYhow, my point is that if I heat up the extruder and don’t immediately start to print it will take a while to fill the nozzle, which means the raft gives the extruder sufficient time to get going before the part is being printed.  Rather than print a raft, waste the plastic, and then have to chip it off later it makes more sense to make sure I advance the extruder a little before I start printing.
  2. Skeinforge->Fill->Infill Solidity (ratio): 0.4->0.3
    • I’ve printed with as little as a 20% fill with no noticeable problems.  I suppose it would really depend on your model.  If the top of the model begins to taper up to a point, then you could probably print with 0% fill.  However, if the top of your build is flat, the topmost layers won’t have much to rest on and will sag just a little.  This doesn’t appear to be a structural problem, but more of an aesthetic one.
  3. Skeinforge->Fill->Infill Begin Rotation (degrees): 45.0->90.0
    • I tried reprinting Zaggo’s whistle in PLA and it didn’t come out – just like it didn’t come out in ABS.  I’m not sure how or why, but my infill rotation got set to 45.  I figure I might have a more solid fill/wall if I had this rotate to 90 degrees.  We’ll find out!
  4. Skeinforge->Fill->Solid Surface Thickness (layers): 3->4
    • This was just a slight tweak to see if I could make solid layers slightly more solid and waterproof/airtight.

Working out

I would have thought that the PLA would have just worked out all of the black ABS out of the way already, but it’s still got the occasional black streak.  Again, I don’t mind – I kinda like it.  However, I would like to be able to build some pieces out of pure PLA.  No matter, I’ll keep printing stripey non-cosmetic parts.  :)

PLA success?!

I figured, what the hell – I built it and I can (probably) repair it, right?

So, I backed out the black ABS I have been printing in, jammed in some freaking sweet PLA, ramped up the heat on the extruder to the exact settings I use for ABS, and then FIRE THE MAKERBOT!

For comparison’s sake I used the same exact settings, same exact Gcode file from the last single walled test piece.

What did it look like, pray tell?

I thought you’d never ask.

PLA printing success!

PLA printing success!

Dragging my feet on PLA

I’ve been a total slacker about getting started printing in PLA.  Part of the reason is I’ve seen others have a lot of problems printing with it – ruining extruders, oozing out of barriers, too hot, too cold, too just right, the heat is uneven, the barrel jams, etc, etc.  However, since I’ve been printing larger and larger objects I’m finding that warpage is become more of an issue.  This means I need to either buy/make a heated platform for the ABS or I need to switch to PLA.

There’s a few things I’d like to build that are big and flat.  I’d like to print up a modular chess board (already have it designed in my head, I just need to export it to Sketchup) and crank out a few Mendel or Mini Mendel pieces.

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